Great questions: Here's what I know:
Regiment:
Regimental commitments will generally end about the time they walk across the stage and shake hands w/Adm (Graduation).
Company:
Plebes will generally stay with the company they are assigned to. (Subject to availability.. it is pretty rare, but if some rebalancing needs to occur, then they might shift a few around. I don't personally know that this has happened, but there's a lot of construction, and if a room or two isn't ready for some reason when the rest of the class returns, they'll need to put them somewhere... temp or perm, I can only guess).
The D/Is will move back to their originating company.
Splits:
Splits will be influenced by any sport they may participate in. Your kid will need to be on campus during that sport's season.
A or B, are the two type of splits. And, defying a seeming logical progression and my learning the alphabet in grade school, B come before A
(B goes to sea first.) So, just remember B=before, A=after
There IS some logic behind it all. But from the outset, it appeared like Company assignments and Sea Splits were doled out by the Magic Sorting Hat from Harry Potter (sorry, just saw the new HP movie last night).
Roommate:
They will shuffle with alarming regularity. I would always ask what room he was in. Irrelevant. All I really needed to know was his Mailbox #. THAT never changes. Note: Some rooms are larger, and hold more than 2 people. They aren't that many of them, so your plebe will likely only have 1 other person in the room.
PT:
They will regularly have physical test. I think once per TRI they have an official one, check the Regimental Calendar on that. You will become adept at filtering out the details that don't apply.
They WILL be kept busy. And, they WILL keep themselves busy (as part of honing their time management/prioritization.. they will HAVE to, or it will overwhelm them).
They will find what works for each of them. At least one Mid I know likes participating in MarineOps, because waking up and doing an early morning run really helps stay alert and attentive for the rest of the day. (shameless plug for MarineOps program
). They will want to find SOME way of addressing the stress.